Despite encouraging preliminary findings regarding the efficacy of mindfulness and acceptance-based treatments for a range of psychological presentations, we have yet to elucidate mechanisms of action within these treatments. One mechanism through which mindfulness may reduce psychological symptoms and promote functioning is enhancing emotional responding and regulation. In this study, we used multimodal assessment to examine the effects of a brief mindfulness intervention in a laboratory setting on emotional experiences and regulation in response to distressing, positive, and affectively mixed film clips. Although there were no condition (mindfulness vs. control) effects on reports of emotional response or difficulties in regulation after the distressing film clip, participants in the mindfulness condition reported significantly greater positive affect in response to the positive film. Additionally, participants in the mindfulness condition reported more adaptive regulation (approaching significance, medium to large effect size) in response to the affectively mixed clip and significantly less negative affect immediately after this clip, although not after a recovery period. No significant differences emerged between conditions on physiological measures (skin conductance and heart rate) throughout the study.